Memory circuit with automatic precharge function, and integrated circuit device with automatic internal command function

ABSTRACT

According to the present invention, a memory circuit requiring refresh operations a first circuit which receives a command in synchronization with a clock signal, and which generates a first internal command internally and a second circuit which generates a second internal command, e.g., a refresh command, internally in a prescribed refresh cycle. And an internal circuit, according to said first internal command, executes corresponding control through clock-synchronous operations, and when said refresh command is issued, sequentially executes control corresponding to the refresh command and control corresponding to said first internal command through clock-asynchronous operations. According to the present invention, when a refresh timing signal is generated, the refresh operation can be intrupted among the external command operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Division of application Ser. No. 10/830,149 filed Apr. 23,2004, which is a Divisional of application Ser. No. 10/438,927 filed May16, 2003, which is Divisional of application Ser. No. 09/841,611 filedApr. 25, 2001. The disclosure of the prior applications is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a memory circuit which requires periodicrefresh operations, such as dynamic random access memory, and furtherrelates to a memory circuit in which refresh operations are executedautomatically without requiring a refresh command from outside, andwhich is capable of high-speed internal execution of operating commandsfrom outside. This invention also relates to an integrated circuitdevice, which, in addition to external commands, is able toautomatically generate and execute commands internally.

2. Description of the Related Art

Dynamic random access memory (DRAM) is widely used as large capacitymemory. Because DRAM is volatile memory, refresh operations arenecessary.

FIG. 1 is a configurational view of a conventional memory circuit. Theconventional memory circuit has a clock buffer 10 for input of anexternal clock signal CLK1 and generation of an internal clock signalCLK1 in sync with this; a command decoder 11 for input of commands insync with the internal clock signal CLK1; an address buffer 12 for inputof addresses; and a data input/output buffer 13 for data input andoutput. In addition, a control circuit 14 controls operations of amemory core 15 in response to commands CMD input by the command decoder11. Operations of the memory core are also controlled in sync with theinternal clock signal CLK1.

Such clock-synchronous DRAM (SDRAM) has, as refresh operations,auto-refresh and self-refresh. Auto-refresh is a refresh operation whichis performed periodically between normal read and write operations, andis executed by means of an auto-refresh command supplied from outside.That is, when an auto-refresh command is input from outside, the commanddecoder 11 generates an auto-refresh command AR1, and in response to AR1the refresh control circuit 16 generates an internal refresh commandREF. By means of this internal refresh command REF, the control circuit14 controls the refresh operation. A selector 18 selects the addressfrom the refresh address counter 17 and outputs the address to theaddress latch circuit 19.

On the other hand, self-refresh is a refresh operation in which thememory device itself executes the refresh operation while in thepower-down mode state, in response to refresh timing automaticallygenerated by an internal oscillator OSC. In the power-down mode state,no commands (read or write) are supplied from outside, and so therefresh control circuit 16 generates an internal refresh command REF inresponse to refresh timing generated with arbitrary timing. Thus, thecontrol circuit 5 14 controls the refresh operation.

In this way, commands are supplied from outside while in the normaloperating state, and refresh commands are also supplied from outside andrefresh operations executed in response. While in the power-down state,no commands are supplied from outside, and so refresh timing isautomatically generated internally and refresh operations are executed.

In this way, in conventional memory circuits the memory controller whichcontrols the memory circuit must control the refresh timing during theinterval of the normal operating state. That is, the memory controlleris equipped with a timer, and must issue auto-refresh commands to thememory circuit each time the refresh timing occurs. Hence, a problemwith the memory controller is the complexity of memory circuit control.

In conventional memory circuits, the control circuit 14 executes controlin response to read and write commands supplied in sync with the clocksignal. Here, if the control circuit 14 is executing the previousinternal operation, the next internal operation is executed in responseto the newly supplied command, regardless of previous internaloperations. Memory circuits have also been proposed in which, if duringexecution of the previous internal operation a new command is suppliedfrom outside, that command is refused.

In the above latter case, refusal of a command from the memorycontroller is undesirable, and so memory circuits generally executeinternal operations as-is in response to supplied commands, as in theformer case. Hence, in the normal operating state, if a refresh commandis issued autonomously within the memory circuit and refresh operationsare executed, a command supplied during these operations may disturb therefresh operation. And if, as in the latter case, a supplied command isrefused, control by the memory controller becomes even more complex.

SUMMARY OF THE INVENTION

Hence, one object of this invention is to provide a memory circuitcapable of automatically executing refresh operations without receivingrefresh commands from the memory controller.

Another object of this invention is to provide a memory circuit which,in normal operation, can automatically execute refresh operationswithout requiring refresh commands from outside, and which can alsorapidly execute internal operations in response to normal commands fromoutside.

Yet another object of this invention is to provide an integrated circuitdevice capable of automatically issuing internal commands in addition toreceipt of externally supplied commands, and of executing internalcommands without disturbing operations corresponding to external 5commands.

In order to achieve the above objects, in a first aspect of thisinvention, an integrated circuit device comprises a first circuit whichreceives commands in sync with a clock signal and which internallygenerates a first internal command, and a second circuit whichinternally generates a second internal command in a prescribed cycle.The internal circuit executes internal operations in accordance with thefirst internal command through clock-asynchronous operations, and when asecond internal command is issued, sequentially executes internaloperations corresponding to the second internal command and internaloperations corresponding to the first internal command throughclock-asynchronous operations.

In a more preferred embodiment, the above integrated circuit device is amemory circuit which requires refresh operations; the above firstinternal command is a read or a write command; the above second internalcommand is a refresh command; and the internal circuit is a memorycontrol circuit. That is, in this embodiment, in the normal state thememory control circuit executes control operations corresponding to thefirst internal command through clock-synchronous operations, inaccordance with commands received in sync with the clock signal. When arefresh command is generated internally as the second internal command,the memory control circuit, in clock-synchronous operation, sequentiallyexecutes control operations corresponding to this refresh command andthe first internal command. When internal operation cycles finally catchup to external operation cycles, the memory control circuit againexecutes control operations for the first internal command throughclock-synchronous operations.

In another preferred embodiment, the integrated circuit device furthercomprises an internal clock generation circuit which generates a firstinternal clock signal in sync with an external clock signal and a secondinternal clock signal faster than the external clock signal. Theinternal circuit executes an internal operation corresponding to thefirst internal command in sync with the first internal clock signalduring a normal state, and executes internal operations corresponding tothe first internal command and internal operations corresponding to thesecond internal command in sync with the second internal clock signalwhen the second internal command is generated.

The first aspect of the invention can be applicable to asynchronousmemory circuit. In this case, a specification of the memory circuitdefines a minimum external command cycle according to which externalcommands are permitted to be supplied. And a memory controller has aninternal operation cycle shorter than the minimum external commandcycle. The memory control circuit executes an internal operation inresponse to the external command during a normal state, and executesinternal operations-continuously according to the internal operationcycle.

A second aspect of this invention is a clock synchronous integratedcircuit device having, for every M external operation cycles (M≧2), Ninternal operation cycles, where N is greater than M (M<N<2M). For Mexternal operation cycles, at most M internal operation cyclescorresponding to M external commands, and at least one internaloperation cycle corresponding to an internal command and not to anexternal command, are assigned. That is, by making internal operationcycles slightly shorter than external operation cycles, it is possibleto execute internal commands which may occur within expanded operationcycles consisting of M external operation cycles.

In a more preferred embodiment of the above second aspect, applicationis to a memory circuit requiring refresh operations. In this case, whena refresh command is generated internally during expanded operationcycles consisting of M operation cycles, (N-M) internal operation cyclesare utilized to execute the refresh operation. These (N-M) cycles arethe difference during expanded operation cycles between the number ofinternal operation cycles N and the number of external operation cyclesM. However, by holding the latency from the input of the externalcommand until read data output to several clock cycles, it is possibleto continuously output read data, to an external memory controller,corresponding to continuous external commands.

In the memory circuit of the above preferred embodiment, an internalclock generation circuit is provided which generates, during an expandedoperation cycle consisting of M external clock cycles, N internalclocks. An external command is input in sync with the external clocksignal (or after waiting for a prescribed phase difference), and theinternal command is generated in sync with the internal clock signal.Read data is output from the memory core in sync with the delayedinternal clock signal, and is output from the data output terminal insync with the external clock signal. Similarly, write data is input fromthe data input terminal in sync with the external clock signal, and isinput to the memory core in sync with the internal clock signal. Hence,the phase difference between the external clock signal and internalclock signal is absorbed by the command and data input/output circuitunits.

In the other preferred embodiment of the above second aspect,application is similarly to a memory circuit in which refresh operationsare required. In this case, when a refresh command is generatedinternally during an expanded operation cycle consisting of M operationcycles, (N-M) internal operation cycles are utilized to execute therefresh operation. Further, the refresh operation can be divided into aplurality of internal operation cycles and executed. Thus, the latency(access time) from input of the external command until output of theread data can be shortened, and high-speed operation can be ensured.

In another preferred embodiment, when refresh operations are dividedinto operations involving word-line driving and operations involvingwriting to memory cells, when the refresh address during a refreshoperation (row address) and the address of subsequent read or writeoperations (row address) coincide, data read out and held during thefirst half of the refresh operation is used as readout data forsubsequent read or write operations. Thus, even though data in memorycells is destroyed during the first half of the refresh operation, thereare no impediments to subsequent operations.

A third aspect of this invention is characterized in that, when in theabove second aspect the external clock signal controlling input ofexternal commands has a shorter cycle than the external operation cycle,a second internal operation cycle is generated according to the externalcommands input in sync with the external clock signal. Hence, when thisthird aspect is applied to a memory circuit, the refresh commandgeneration circuit generates refresh commands according to the state ofinput of external commands.

By means of this third aspect, even in the case of an integrated circuitdevice or memory circuit installed in a high-speed clock system, asecond internal operation cycle 5 can be autonomously generated andexecuted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configurational view of a conventional memory circuit;

FIG. 2 is an overall configurational view of the memory circuit in afirst embodiment of this invention;

FIG. 3 is a drawing showing clock-synchronous operation andclock-asynchronous operation;

FIG. 4 is a drawing showing an example of the configuration of thememory control circuit 14;

FIG. 5 is a timing chart which shows a transmission fromclock-synchronous operation to clock-asynchronous operation when arefresh command is generated;

FIG. 6 is a timing chart which shows clock synchronous operation andclock-asynchronous operation in the first embodiment;

FIG. 7 is a timing chart which shows clock synchronous operation andclock-asynchronous operation in the case of a slower external clock;

FIG. 8 is a timing chart which shows clock-synchronous operation andclock-asynchronous operation in the case of a still slower externalclock;

FIG. 9 is a timing chart which shows clock-synchronous operation andclock-asynchronous operation in the case in which internal operationcycles are twice as 5 long as the external clock CLK1 cycles;

FIG. 10 is a configurational view of the memory circuit in a secondembodiment of the invention;

FIG. 11 is an operation timing chart of the memory circuit of the secondembodiment;

FIG. 12 is an operation timing chart for the case in which read commandsand write commands are intermixed;

FIG. 13 is a circuit diagram for the clock generation circuit;

FIG. 14 is an operation timing chart for the clock generation circuit;

FIG. 15 is a drawing showing the refresh command generation circuit andthe operation timing chart thereof;

FIG. 16 is a configurational view of the memory circuit in a thirdembodiment of the invention;

FIG. 17 is a drawing explaining the refresh operation of the thirdembodiment;

FIG. 18 is a drawing explaining the refresh operation of the thirdembodiment;

FIG. 19 is an operation timing chart for the third embodiment;

FIG. 20 is a drawing showing the clock generation circuit applied to thethird embodiment;

FIG. 21 is an operation timing chart for the clock generation circuit;

FIG. 22 is a drawing showing the refresh command generation circuitapplied to the third embodiment, and 5 the operation timing chartthereof;

FIG. 23 is a drawing showing the refresh command generation circuit inthe power-down state and the operation timing chart thereof;

FIG. 24 is a drawing showing the memory circuit of a fourth embodimentof this invention;

FIG. 25 is an operation timing chart of the fourth embodiment;

FIG. 26 is an operation timing chart of the fourth embodiment;

FIG. 27 is an operation timing chart of the fourth embodiment;

FIG. 28 is an operation timing chart of the fourth embodiment;

FIG. 29 is a drawing showing the clock generation circuit applied to thefourth embodiment;

FIG. 30 is an operation timing chart of the clock generation circuit ofFIG. 29;

FIG. 31 is another clock generation circuit applied to the fourthembodiment;

FIG. 32 is an operation timing chart of the clock generation circuit ofFIG. 31;

FIG. 33 is a drawing showing a refresh command generation circuitapplied to the fourth embodiment, and the operation thereof;

FIG. 34 is a drawing showing another command register circuit in thefourth embodiment;

FIG. 35 is an operation timing chart of the memory circuit for the casein which the command register circuit of FIG. 34 is used;

FIG. 36 is an operation timing chart of the memory circuit for the casein which the command register circuit of FIG. 34 is used;

FIG. 37 is a drawing of a clock generation circuit for the case in whichthe command register of FIG. 34 is used;

FIG. 38 is an operation timing chart for the clock generation circuit ofFIG. 37;

FIG. 39 is a configurational view of the memory circuit of a fifthembodiment of the invention;

FIG. 40 is a drawing showing the flow of signals in FIG. 39;

FIG. 41 is an operation timing chart for FIG. 39;

FIG. 42 is a drawing of another command register circuit in the fifthembodiment;

FIG. 43 is a drawing showing the flow of signals in FIG. 42;

FIG. 44 is an operation timing chart for FIG. 42;

FIG. 45 is a drawing showing the relation between external operationcycles to which another clock generation circuit is applied, andinternal operation cycles;

FIG. 46 is a drawing showing another clock generation circuit; and,

FIG. 47 is an operation timing chart for the clock generation circuit ofFIG. 46.

FIG. 48 is a drawing showing a memory circuit according a modificationof the first embodiment.

FIG. 49 is an operation timing chart of the modification of FIG. 48.

FIG. 50 is a drawing showing a memory circuit according to anothermodification of the first embodiment.

FIG. 51 is a timing chart showing an operation of the modification.

FIG. 52 is an operation timing chart in case where the normal operationstate is transferred into the faster operation mode upon generation ofthe internal refresh command.

FIG. 53 is a timing chart of the slow operation mode and the fastoperation mode according to the present modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of this invention are explained hereinbelow, referring tothe drawings. However, these embodiments do not limit the technicalscope of this invention. Further, the embodiments described below areexplained for the example of a memory circuit, but this invention is notlimited to a memory circuit, and can also be applied to generalintegrated circuit devices.

First Embodiment of the Invention

FIG. 2 is an overall configurational view of the memory circuit in afirst embodiment of this invention. Elements which are the same as inFIG. 1 are assigned the same reference numbers. An external clock signalCLK supplied from outside is input to the clock buffer 10, and aninternal clock signal CLK1, synchronized with the clock signal CLK butwith phase shifted slightly, is generated. This internal clock signalCLK1 is supplied to circuits, not shown, including a command decoderregister 11, address buffer register 12, data input/output bufferregister 13, memory control circuit 14, and refresh command generationcircuit 20, contributing to operation in sync with the clock. Theclock-enable signal CKE is a signal indicating the normal state andpower-down state.

In the memory circuit in the first embodiment, the command decoderregister 11 receives a command CMD in sync with the clock signal CLK1,generates a read command RD or a write command WR, and supplies this tothe memory control circuit 14. The refresh command generation circuit 20generates a refresh command REF in response to a refresh timer signalREFTM, generated in a fixed refresh cycle by an internal refresh timer21. In contrast with conventional examples, the refresh commandgeneration circuit 20 responds to the refresh timer signal REFTM whetherin the normal state or in the power-down state, and generates a refreshcommand REF.

The memory control circuit 14 normally executes read control operationsor write control operations through clock-synchronous operations,according to internal RD and WR commands. When a refresh command REF isgenerated, the memory control circuit 14 executes a refresh controloperation or a subsequent internal command control operation, throughclock-asynchronous operations. The control circuit 14 executes controloperations corresponding to commands by supplying to the memory core 15signals such as, for example, word line driving signal, sense amplifieractivation signal, column select signal, and precharge signal.

To this end, when one operation cycle is ended, the memory controlcircuit 14 generates a command reception signal CMDEN to receive thenext command. When, after issuing a command reception signal CMDEN, aninternal command RD, WR, or REF is received, a reset signal RST1 issupplied to the command decoder register 11, a reset signal RST2 issupplied to the refresh command generation circuit 20, and therespective internal commands are reset.

FIG. 3 is a drawing showing clock-synchronous operation andclock-asynchronous operation. FIG. 3A is a drawing which explainsclock-synchronous operation. The commands RD and WR are input,generated, and held by the command register 11 in sync with the clocksignal CLK1. The memory control circuit 14 receives the internalcommands RD and WR held by the command register 11 while the commandreception signal CMDEN is at H level. Then, control operationscorresponding to the internal command are executed.

The memory core 15 has a memory cell array; the minimum operation cycleof this memory cell array consists of a word line rise ta, bit lineamplification tb, word line fall tc, and bit line precharge td. Thesemake up the memory cell array operation interval tmca.

In normal synchronous DRAM, in consideration of scattering due tomanufacturing processes and other factors, even when the memory cellarray operation interval tmca is repeated in sync with the clock signalCLK1, there is a command wait time tl between the memory cell arrayoperation intervals tmca. Hence, as shown in FIG. 3A, even when thememory cell array operation interval tmca has ended and a commandreception signal CMDEN is generated, a new command is not input untilthe command wait time t1 has elapsed. After the new command is input,the internal command is received by the memory control circuit 14, andthe corresponding control operation begins. As a result, the memory cellarray operation interval tmca is repeated in sync with the clock signalCLK1.

Next, FIG. 3B shows the clock-asynchronous operation. The commands RD,WR are either held in sync with the clock signal CLK1, or else a refreshcommand REF, not shown, is generated asynchronously. When the memorycell array operation interval tmca has ended, the internal commands RD,WR, REF are already generated, and so the memory control circuit 14receives the internal command in response to the command receptionsignal CMDEN, and the corresponding memory cell array operation intervalbegins. Hence, in this case, no command wait time tl exists betweenmemory cell array operation intervals tmca, and the memory cell arrayoperations are repeated in the minimum operation cycle.

When performing clock-asynchronous operations, there exists no commandwait time tl, and so even if memory array operations begin with a lagbehind the phase of the clock signal CLK1, by executing a plurality ofcommands with a minimum operation cycle, the memory cell arrayoperations can gradually catch up to the phase of the clock signal CLK1.

In this way, clock-synchronous operations are normal operations, andclock-asynchronous operations correspond to high-speed operations.Switching between these normal operations and high-speed operations caneasily be performed by taking the logical AND of the internal commandheld by the command register 11, and the command reception signal CMDENgenerated at the time of completion of the operation interval. That is,if the command reception signal CMDEN is generated earlier, the memorycell array operation interval is begun according to the internal commandsubsequently generated in sync with the clock signal. Hence, in thiscase, operations are the clock-synchronous operations (normaloperations) of FIG. 3A. On the other hand, if the internal commandexists earlier than CMDEN, the memory cell array operation intervalbegins in response to the subsequently generated command receptionsignal CMDEN, without the wait time tl. In this case, operations are theclock-asynchronous operations (high-speed operations) of FIG. 3A.

When the memory cell array begins operations in response to a command,the command reception signal CMDEN is reset, and the internal command ofthe command register 11 is reset. Also, the refresh command of therefresh command generation circuit 20 is reset.

FIG. 4 is a drawing showing an example of the configuration of thememory control circuit 14. The memory control circuit 14 has a controlsignal generation circuit 24 which supplies various control signals φ tothe memory core 15, and internal command input buffers 25, 26, 27.Control signals include word line driving signals φWL which drive wordlines, bit line transfer gate signals φBTR which drive the bit linetransfer gates between bit line pairs and sense amplifiers, activationsignals φLE which activate sense amplifiers, column gate driving signalsJCL, and precharge signals +PRE.

The memory control circuit 14 also has pulse generation circuits 28, 30,32, 33 which generate pulses at the falling edge of an input pulse, anda flip-flop FF 5 which generates the command reception signal CMDEN.Internal commands RD, WR, REF are, for example, in the inactive state atL level, and in the active state at H level.

FIG. 5 is a timing chart which shows the case when making a transmissionfrom clock-synchronous operation to clock-asynchronous operation when arefresh command is generated. The memory cell array repeats normaloperations, synchronized with the clock, until the rising edge C1 of theclock signal CLK1. Hence, before the clock rising edge C1, the commandreception signal CMDEN is generated. Also, it is assumed that before theclock rising edge C1, the refresh timer signal REFTM is generated.

When the refresh timer signal REFTM is generated prior to the operationcycle 1, the refresh command generation circuit 20 generates a refreshcommand REF after a delay for a prescribed length of time from therising edge C1 of the subsequent clock signal. Thus, an internal commandRD(AO) corresponding to a command from outside is given precedence, andinternal operation cycle thereof can be executed.

Because the command reception signal CMDEN has been received, theinternal command RD(AO) (read command) generated at the rising edge C1is input to the command input buffer 25 of the memory control circuit 14in sync with the clock signal CLK1. Consequently, various controlsignals are generated for the read operation by the control signalgeneration circuit 24, and the cycle 1 starts from the leading edge C1.In the cycle 1, the word line driving signal φWL, sense amplifieractivation signal φLE, column select signal φCL, and other signals aregenerated, and finally the precharge signal φPRE is generated. When theprecharge interval ends, the flip-flop FF generates a command receptionsignal CMDEN. When operations for the internal command RD(AO) are begun,the command is reset by the reset signal RST1.

At this point, a refresh command REF is already generated, and so thecommand input buffer 27 inputs this REF command in response to thecommand reception signal CMDEN, and the control signal generationcircuit 24 generates various control signals φ corresponding to therefresh operation. In actuality, the refresh operation is the same as aread operation. When the REF command is input, a reset signal RESET isgenerated, and the command reception signal CMDEN goes to L level. Atthe same time, a reset signal RST2 is generated, and the refresh commandREF is reset. Hence, the operation of cycle 2 corresponding to therefresh command begins before the clock rising edge C2, without anintervening wait time tl. That is, clock-asynchronous operation occurs.

When the refresh operation ends, a command reception signal CMDEN isagain generated. At this time, the internal command RD(A1) is alreadyheld in the command register 11, in sync with the clock edge C2. Hence,in response to the command reception signal CMDEN, the internal commandRD(A1) is input to the command input buffer 25, and operation of thenext cycle 3 begins. This operation is also a clock-asynchronousoperation.

Subsequently, internal commands generated in sync with the clock edgeare similarly executed through sequential clock-asynchronous operations.Clock-synchronous operation is high-speed operation without wait time,so that the internal operation cycle gradually catches up with the clockCLK1 cycles, and the command reception signal CMDEN advances ahead ofthe phase of the clock CLK1 rising edge. As a result, the internaloperation cycles become clock-synchronous operations, in sync with theclock signal CLK1 and with a wait time t1 in between.

FIG. 6 is a timing chart which shows clock-synchronous operation andclock-asynchronous operation (high-speed operation) in the firstembodiment. FIG. 6 shows the operation of FIG. 5 through more numerousoperation cycles. The command CMD from outside is supplied in sync withthe clock signal CLK1, and internal commands are held by the commandregister 11. In the example of FIG. 6, the read command RD is suppliedcontinuously.

Initially, the internal operation cycles RDO-2 are executed in sync withthe clock signal CLK1. When, at the time of the internal operation cycleRD1, the refresh timer generates a refresh timer signal REFTM, aninternal refresh command REF is output after a fixed delay. When theinternal operation cycle RD2 ends, an internal operation cycle beginsaccording to the existing refresh command REF. Thereafter, a transitionto clock-synchronous operation is made, and internal operation cyclesRD3 to RD7 are high-speed operations. When internal operation cycleseventually catch up to the clock CLK1 cycles, the internal operationcycle RD8 and subsequent cycles again become clock-synchronousoperations.

That is, in response to continuously input read commands, all are inputand held, when necessary refresh operation cycles are interrupted, andthe held read commands are executed through clock-asynchronoushigh-speed operations. Consequently, the read data is outputcontinuously to the data output terminal DQ, and the memory controllerdoes not “see” the internal refresh operations; it appears that normalcontinuous reading is being performed.

FIG. 7 is a timing chart which shows clock-asynchronous operation andclock-asynchronous operation 25 (high-speed operation) in the case of aslower external clock. In this case, internal high-speed operation(clock-synchronous operation) cycles are considerably shorter than clockCLK1 cycles. Hence, clock-asynchronous operation begins from a refreshoperation cycle REF after generation of a refresh command REF; but thishigh-speed operation continues until the next read operation cycle RD3,after which clock-synchronous operation occurs. That is, after executionof refresh operation, the interval until internal operation cycles catchup with clock CLK1 cycles is shortened.

FIG. 8 is a timing chart which shows clock-asynchronous operation andclock-asynchronous operation (high-speed operation) in the case of astill slower external clock. In this case, after the third readoperation cycle RD, a refresh operation is performedclock-asynchronously; but this refresh operation is completed before thenext clock CLK1 rising edge, and from the next read operation cycle,operation returns to clock-synchronous operation.

In all of the cases of FIGS. 6, 7 and 8, internal circuits arecontrolled such that read data is output to the data output terminal DQtwo clock cycles after input of the external command, so that even whencontinuous commands during normal operation are interrupted by refreshoperations during processing, read data can be output continuouslywithout problem.

FIG. 9 is a timing chart which shows clock synchronous operation andclock-asynchronous operation (high-speed operation) in the case in whichinternal operation cycles are twice as long as the external clock CLK1cycles. This is an example for cases in which the clock CLK1 in thesystem equipped with the memory device is fast, and compared with this,operations within the device are slow. In this case, specifications aresuch that the continuous supply of commands from outside in sync withthe external clock CLK1 is not permitted. Hence, at the fastest,commands from outside are supplied in sync with odd-numbered or witheven-numbered clock rising edges.

Even in this case, as shown in FIG. 9, the wait time tl between internaloperation cycles can be utilized, similarly to the case of FIG. 6, sothat a refresh operation cycle can be inserted. However, in the case ofFIG. 9, read data is output to the data output terminal DQ four clockcycles after input of the external command. There are also cases inwhich, after a command has been input in sync with an odd-numbered clockcycle, the command is supplied in sync with an even-numbered clockcycle. However, even in this case, commands are not supplied in syncwith continuous clock cycles. Hence, in this case, two clock cyclesexist between commands, and there is no impediment to the insertion ofan internal refresh operation cycle.

In the above first embodiment, the refresh timer signal REFTM is at, forexample, a frequency approximately two orders of magnitude lower thanthe clock signal CLK. Hence, for several hundred clock cycles CLK, therefresh timer signal REFTM is generated once or so. As a result, forseveral hundred external operation cycles, there are internal operationcycles in which one refresh cycle is added to several hundred cycles.There is no need to allocate two types of internal operation cycle,normal internal operation cycles and refresh operation cycles, to allexternal operation cycles, and high-speed operation is assured in normaloperation.

Second Embodiment of the Invention

The second embodiment of this invention is a memory circuit, whichexecutes commands through internal operation cycles, which are shorterthan external operation cycles. In a memory circuit which requiresrefresh operations, the memory control circuit has, for every M externaloperation cycles (Ma2), N internal operation cycles, where N is greaterthan M (M<N<2M). External commands are input in sync with externaloperation cycles. Read data output and write data input are alsoperformed in sync with external operation cycles. However, the Ninternal operation cycles have first internal operation cycles, whichexecute external commands corresponding to external operation cycles,and second internal operation cycles which execute refresh commands.When refresh commands are issued internally, the above second internaloperation cycles are used to perform refresh operations.

In this way, the memory circuit of the second embodiment generates,within an expanded operation cycle consisting of M external operationcycles, N internal operation cycles, where N is greater than M, and byutilizing the (N-M_internal operation cycles, executes refresh operationcorresponding to refresh commands which are automatically generatedinternally. However, commands and write data are input, and read dataoutput continuously in sync with external operation cycles in responseto continuously input read commands, with a delay of a prescribed readlatency.

In the following embodiment, the case of M=7 and N=8 is explained.

FIG. 10 is a configurational diagram of the memory circuit in the secondembodiment of the invention. Elements, which are the same as in FIG. 2,are assigned the same reference numbers. FIG. 11 is the operation timingchart. Compared with FIG. 2, the memory circuit of FIG. 10 differs inbeing provided with a clock generation circuit 35, which generates aclock signal ECLK1 from the external, internal clock ECLK, and in syncwith the external clock, and international clock signals ICLK1 to ICLK3and REF-CLK which control internal operation cycles. As shown in FIG.11, internal clock ICLK defines eight internal operation cyclesoccurring for every seven external operation cycles. Hence, the periodof the internal clock cycles is slightly shorter than the period ofexternal clock cycles.

Among the clock signals generated by the above clock generation circuit35, the external clock signal ECLK1 is synchronized with the externalclock signal ECLK, and controls the input and output timing of commands,addresses, and data. The internal clock signal ICLK1 controls the startof internal operation cycles to execute external commands. The internalclock signal ICLK2 lags behind the above clock signal ICLK1, and outputsdata read from the memory core to the data bus BD2. The output latchclock ICLK3 receives data output of the data bus DB2 into the outputregister 134 within the data input/output circuit 13. The refresh clocksignal REF-CLK controls refresh internal operation cycles.

Hence, in the memory circuit of FIG. 10, external commands CMD are inputto the command decoder 11A and external addresses are input to theaddress buffer 12A, both in sync with the clock signal ECLK1. In thedata input/output buffer 13, read data is output from the output buffer133 and write data is input to the input buffer 131, in sync with theclock signal ECLK1.

The command register 11B and address register 12B supply commands RD, WRand external addresses EAdd to the memory control circuit 14 and memorycore 15 in sync with the internal clock signal ICLK1. Similarly, readdata is output from the memory core to the sense buffer in sync with theinternal clock signal ICLK2, and read data in the data bus is latched bythe register 134 in sync with the output latch clock ICLK3. Write datais latched by the register 132 in sync with the internal clock signalICLK1. Hence, the registers 11B, 12B, 134 and 132 absorb phase shiftsbetween the external clock signals and internal clock signals, and latchand transmit corresponding signals in accordance with internal operationcycles.

The timing chart of FIG. 11 shows the case in which, as externalcommands, the read commands Read-0 to Read-12 are supplied in sync withthe external clock ECLK. A cycle consisting of seven external clockcycles ECLK is called an expanded operation cycle. In this expandedoperation cycle, seven internal clock cycles ICLK1 and one refresh clockcycle REF-CLK are generated.

First, in sync with the external clock signal ECLK1, an external commandis input to the command decoder 11A and the external address is alsoinput to the address buffer 12A. The first read command Read-0 islatched by the register 11B in sync with the internal clock signalICLK1, and is supplied to the memory control circuit 14. Then, the readoperation cycles are executed in sync with the internal clock signalICLK1. Read data which is read from the memory core 15 is output to thedata bus DB2 by the sense buffer SB in sync with the internal clocksignal ICLK2, and is latched by the output register 134 in sync with theoutput latch clock ICLK3. Finally, the read data is output to the outputterminal DQ from the output buffer 133 in sync with the external. clocksignal ECLK1. In the example of FIG. 11, the latency from input of thefirst read command Read 0 to output of the read data QO is two externalclock cycles.

In the example of FIG. 11, the second internal operation cycle withinthe expanded operation cycle is allocated as a refresh operation cycle.Hence, the refresh clock signal REF CLK is generated as the secondinternal clock signal. The refresh command generation circuit 20generates a refresh command REF in sync with the refresh clock signalREF CLK, in response to the refresh timer signal REFTM generated at eachrefresh cycle by the refresh timer 21. Hence, when the refresh timersignal is generated, the refresh operation is executed in the secondinternal operation cycle within the expanded operation cycle. In therefresh operation, the selector 18 selects the refresh address RAdd ofthe refresh address counter 17 and supplies it to the row decoder RDEC.When the refresh operation is executed, the refresh address counter 17is incremented. If no refresh timer signal is generated, no operationsare performed in the second internal operation cycle. In the thirdthrough the eighth internal operation cycles, read operationscorresponding to the remaining six read commands, Read 1 to Read 6, areexecuted.

Hence, compared with external operation cycles (the cycles of theexternal clock ECLK), internal operation cycles subsequent to aninserted refresh operation lag considerably; but because internaloperation cycles are each ⅛ shorter than external clock cycles, theinternal operation cycles gradually approach the external clock cycles,and finally catch up at the end of the expanded operation cycle.

FIG. 12 is an operation timing chart for the case in which read commandsand write commands are intermixed. In this case also, similarly to thecase of FIG. 11, there exist eight internal operation cycles for sevenexternal clock cycles. Write data D2 is input in sync with the externalclock ECLK1, and write operations are executed in sync with internaloperation cycles. Because the read latency is 2, the next write commandWrite 2 is supplied four clock cycles after the read command Read 1.Thus, conflicts between read data Q1 and write data D2 at theinput/output terminal DB are avoided.

FIG. 13 is a circuit diagram for the clock generation circuit. FIG. 14is the operation timing chart thereof. The clock generation circuit 35inputs the external clock signal ECLK to the input buffer 39, and viathe pulse width adjustment circuit 40, generates a clock signal ECLK1having a pulse width equal to three gates' worth from the rising edge.Hence, this clock signal ECLK1 is synchronized with the external clockECLK, and lags somewhat in phase.

The output N1 of the pulse width adjustment circuit 40 is supplied toone input of the phase comparator 41, and is also supplied to the otherinput via the variable delay elements D1 to D8. In response to the phasedifference detected by the phase comparator 41, the delay controlcircuit 42 outputs a delay control voltage Vc such that the phasedifference disappears. The delay times of each of the variable delayelements D1 to D8 are adjusted according to this delay control voltageVc.

Hence, as the output of the variable delay elements, eight internalclock signals N1 to N8 are generated, having phase shifts resulting fromdivision of one cycle of the external clock ECLK into eight equal parts.These internal clock signals N1 to N8 are selected by the multiplexer 38according to select signals S1 to S8 output by the shift register 37,and are output as the internal clock signal N10. The shift register 37is shifted by the falling edge of the internal clock signal N10. Theselect signals S1 to S8 generated in sequence select the internal clocksignals N1 to N8 in the order S1, S8, S7, . . . , S2. As a result, theinternal clock signal N10 is a short-cycle clock having ⅞ the cycle ofthe external clock ECLK, and with phase advanced by ⅛ cycle relative tothe external clock ECLK.

From this internal clock signal N10, the second clock cycle iseliminated by the NOR gate 44, so that seven internal clocks ICLK1 aregenerated. Further, the second clock is selected by the NAND gate 43,and one refresh clock signal REF CLK is generated. An internal clocksignal ICLK2 is generated, with phase lagging by the delay time of thevariable delay elements D9 through D12 with respect to the internalclock ICLK1. From the clock N4, an output latch clock ICLK3 is generatedwith phase lagging by two inverter stages' worth. By selecting the clockN4, C1 and C2 of the internal clock ICLK2, and C3, C4, C5 of the outputlatch clock ICLK3, are generated in the order C3 C1 C4 C2 C5. Thus, evenwhen a refresh operation is inserted in the second internal operationcycle, the output register 134 can be latched continuously in the sameorder as the read data in response to continuous read commands.

FIG. 15 is a drawing showing the refresh command generation circuit andthe operation timing chart thereof. The refresh command generationcircuit 20 has delay flip-flops 46, 47; a NAND gate 48; and a delaycircuit 49. As shown in the operation timing chart, the signal N22 goesto H level in sync with the refresh clock signal REF CLK followinggeneration of a refresh timer signal REFTM, and a refresh command REF isgenerated. After the delay of the delay circuit 49, the count up signalUP is generated, and the address of the refresh address counter 17 isincremented. Thus, the flip flops 46, 47 are reset.

In this way, of the eight internal operation cycles within the expandedoperation cycle, the second internal operation cycle is reserved forrefresh operations. When the refresh timer signal REFTM is generated, arefresh command REF is generated in the immediately following secondinternal operation cycle, and refresh operations are executed in thememory core 15. In these refresh operations, word lines are drivencorresponding to the refresh address RAdd from the refresh addresscounter, and data read to bit line pairs is amplified by the senseamplifier SA and rewritten to the memory cells. Then word line levelsare lowered, and precharge operations are performed.

Third Embodiment of the Invention

In the second embodiment, the second internal operation cycle wasallocated as a refresh operation cycle. Hence, the read access time(read latency) of read commands corresponding to the first internaloperation cycle was, as shown in FIG. 11, relatively long. This isbecause the output timing of read data in cycles before and after thesecond internal operation cycle is made continuous in sync with theexternal clock.

On the other hand, in the third embodiment of this invention, amongeight external operation cycles, there are eight first internaloperation cycles for execution of external commands, and two secondinternal operation cycles to perform refresh operations. The secondinternal operation cycles for refresh operations are of approximatelyhalf the length of the first internal operation cycles, and a singlerefresh operation is divided into two second internal operations. As aresult, the worst read access time can be shortened compared with 5 thesecond aspect.

FIG. 16 is a configurational diagram of the memory circuit in the thirdembodiment of the invention. Differences with FIG. 10 include thegeneration of two refresh commands REF1, REF2, and the provision of acomparator 50 which compares the refresh address RAdd and the externaladdress Eadd and generates a comparison result signal. Thisconfiguration also differs from FIG. 10 in that within the memory core15 are provided a data register DRG which temporarily holds memory cellread data, and a transfer gate TRG provided between bit line pairs (notshown) within the cell array MCA, and the data register DRG. The dataregister DRG, which is essentially the same circuit as the senseamplifier SA, amplifies and holds the voltage of bit line pairs in thefirst half of the refresh operation cycle. Otherwise, the same referencenumbers have been assigned, and so explanations are omitted.

FIGS. 17 and 18 are drawings, which explain refresh operations in thethird embodiment. FIG. 17A shows a normal refresh operation and a reador write operation. In either case, a word line WL selected by a rowaddress is driven, and data in memory cells is read to bit line pairsBL, /BL; this is amplified by the sense amplifier SA, and afterrewriting, precharging is performed.

FIG. 17B shows a refresh operation in this embodiment. Refreshoperations in this aspect are divided into two refresh operation cyclesREF1, REF2 and executed. In the initial refresh step 1, the word line isdriven and memory cells for refreshing are selected, and this data istransferred to the data register DRG via bit line pairs and the transfergate TRG. The data register DRG is essentially the same circuit as thesense amplifier, can amplify the voltage on bit line pairs, and holdsthis data. Next, in refresh step 2, the memory cells for refreshing areagain selected, and data held by the data register is rewritten tomemory cells via the transfer gate. In both refresh steps, prechargingis performed lastly. Further, between the two refresh steps are insertednormal read or write operation cycles corresponding to externalcommands.

FIG. 18 shows another refresh operation of this aspect. By dividing therefresh operation into two refresh cycles, in the initial refresh step1, the data of the memory cells for refreshing is destroyed. In refreshstep 2, following several internal operation cycles, rewriting from thedata register is performed; but if, in normal internal operation cyclesduring this interval, row addresses which are the same as the refreshedmemory cells are accessed, read and write operations cannot be performednormally.

Hence, as shown in FIG. 18, when the row address of refreshed memorycells Aa and the row address of subsequent normal internal operations Aacoincide, in the internal operation cycle, the transfer gate TRG isopened, and data held by the data register DRG is read, or datacorresponding to write data from the write amplifier WA is written tothe data register DRG. Hence, in this internal operation cycle, it isnot always necessary to drive word lines.

In the subsequent refresh step 2, word lines are driven, the transfergate TRG is again opened, and data held in the data register DRG iswritten to memory cells via bit line pairs. Thus, rewriting in readoperations, and rewriting in write operations, are performed.

To this end, an address comparator 50 is provided as shown in FIG. 16,and the memory control circuit 14 controls opening and closing of thetransfer gate TRG according to the comparison result signal. An enablesignal EN is output to this address comparator 50 only during theinterval between the initial refresh command REF1 and the next refreshcommand REF2, and during this interval refresh address RAdd and externaladdresses EAdd are compared.

FIG. 19 is an operation timing chart for the third embodiment. Teninternal operation cycles are generated for eight external operationcycles. on the second and the seventh internal cycles, the refreshoperation cycles divided into two, RefI a and Ref2 a, are executed.Hence, refresh operation cycles are executed after every four normalinternal operation cycles to execute external commands. Moreover,because refresh operations are divided into two cycles, individualrefresh operation cycles end in approximately half the time of a normalinternal operation cycle. As a result, the access time for a readcommand Read 0 is shortened compared with FIG. 11. This is because thetime of the refresh operation cycle RefI a following the internaloperation cycle Read 0 is short, so that even if output data QO from theinternal operation cycle Read 0 and output data Q1 from the followinginternal operation cycle Read 1 are made continuous, the output data QOneed not be delayed so much.

As shown in FIG. 19, for eight external clock cycles ECLK, eightinternal clock cycles ICLK1 controlling execution of external commandsand two refresh clock cycles REF CLK are generated. Thus, ten internaloperation cycles are generated.

FIG. 20 is a drawing showing the clock generation circuit 35 applied tothe third aspect. The same reference numbers as in FIG. 13 are assigned.FIG. 21 is the operation timing chart thereof. In contrast with theclock generation circuit of FIG. 13, in the clock generation circuit ofFIG. 20, the shift register 37 has a five stage configuration. Selectsignals S1, S5, S4, S3, S2 generated by the shift register 37 areapplied to the multiplexer 38, and N1, N8, N4, N3, N2 are selected inthat order as the internal clock signal N10. Hence, for four externalclock cycles ECLK, five internal clock cycles N10 are generated.

The internal clock cycle N10 with the timing of the clock signal N8 isselected by the NAND gate 43, and the refresh clock signal REF CLK isgenerated. The internal clock cycle N10 with the timing of the clocksignal N8 is removed by the NOR gate 44, and an internal clock signalICLK1 to begin internal operation cycles is generated. The internalclock signal ICLKI is delayed by the delay elements D9 to D12, to becomeanother internal clock signal ICLK2. In FIG. 20, the circuit, whichgenerates the output latch clock signal ICLK3, is omitted.

FIG. 22 is a drawing showing the refresh command generation circuitapplied to the third embodiment, and the operation timing chart thereof.Compared with the refresh command generation circuit applied to thesecond embodiment shown in FIG. 15, the refresh command generationcircuit of FIG. 22 has flip flops 60, 61, 62 and a NAND gate 63 added.Hence, by means of the flip-flops 46, 47 and NAND gate 48, after arefresh timer signal REFTM is generated, the first refresh command REF1is generated in sync with the next refresh clock cycle REF CLK. And,through the use of the flip flops 60, 61, 62 and NAND gate 63, after therefresh timer signal REFTM is generated, the second refresh command REF2is generated in sync with the second refresh clock cycle REF CLK. And,through the use of the refresh flip flop 64, in the interval after thefirst refresh command REF1 is generated and until the second refreshcommand REF2 is generated, a comparator enable signal EN is generated.After the second refresh command REF2 is generated, a count up signal upis generated via the delay circuit 49.

In the second embodiment shown in FIG. 10 and the third embodiment shownin FIG. 16, the clock enable signal CKE is supplied from outside. Thisclock enable signal CKE is a signal that indicates the normal operationstate and power down state. That is, when the clock enable signal CKE isat H level, the state is the normal operation state (active state), andwhen at L level, the state is the power down state. In the power downstate, the clock generation circuit 35 stops generation of the differentclock signals. As a result, the command, address, and data input/outputcircuits, to which the external clock signal CLK1 is supplied, stopinput and output of external signals. Further, the memory controlcircuit 14 also stops operations corresponding to external commands.

FIG. 23 is a drawing showing the refresh command generation circuit inthe power down state and the operation timing chart thereof. Comparedwith the refresh command generation circuit of FIG. 15, NAND gates 66,67 are added, and a clock enable signal CKE is supplied.

As shown in the timing chart, in the normal operation state in which theclock enable signal CKE is at H level, similar to FIG. 15, after therefresh timer signal REFTM is generated, a refresh command REF isgenerated in sync with the refresh clock signal REF CLK. On the otherhand, in the power down state in which the clock enable signal CKE is atL level, when a refresh timer signal REFTM is generated a refreshcommand REF is generated. This is because in the power down state, norefresh clock signal REF CLK is generated.

Fourth Embodiment of the Invention

In the second and third embodiments, external operation cycles andexternal clock cycles are the same. However, integrated circuit devicesand memory circuits which are mounted in a system synchronized with afast clock signal must perform internal operations in response to a highspeed external clock which has cycles shorter by a factor of two or morethan internal operation cycles. In these cases, external operationcycles are of lengths adjusted to the internal operation cycles of theintegrated circuit device or memory circuit.

The fourth embodiment is a memory circuit applied to a case in which,for example, the external operation cycle is 20 ns, whereas the externalclock cycle is 10 ns. That is, this memory circuit is capable ofoperating at an external operation cycle with frequency of 50 MHz, andmoreover can be mounted in a system with a clock cycle with frequency of100 MHz. In such a case, a system operating with a fast clock isconstrained to an interval of two clock cycles or more between commandinputs, in coordination with the operation cycles of the memory circuit.Hence, even the fastest command input is limited to input of externalcommands in sync with every other external clock cycle. Externalcommands are permitted to be input in sync with either odd numberedexternal clock edges or even numbered external clock edges. As a result,when, after an external command is supplied at an odd-numbered clockedge, the next external command is supplied at an even numbered clockedge, two external clock cycles must be inserted therebetween.

FIG. 24 is a drawing showing the memory circuit of the fourth embodimentof this invention. FIGS. 25 to 28 are operation timing charts of thefourth embodiment. FIG. 25 shows basic operation; FIG. 26 showsoperation when an external command is input on the phase “a” side of theexternal clock signal ECLK; FIG. 27 shows operation when an externalcommand is input on the phase “b” side of the external clock signalECLK; and FIG. 28 shows operation when external commands are inputrandomly on both the phase “a” and “b” sides of the external clocksignal ECLK.

Thus, in the fourth embodiment, there exist two types of phase relationbetween external operation cycles and internal operation cycles. Thatis, there are the two types shown in FIGS. 26 and 27. Hence, when, asshown in FIG. 26, an external command is input on the phase “a” side, ofthe eight internal operation cycles generated within the expanded cycleconsisting of seven external operation cycles, the second internaloperation cycle is allocated to refresh operations. On the other hand,when as shown in FIG. 27 an external command is input on the phase “b”side, of the eight internal operation cycles, the sixth internaloperation cycle is allocated to refresh operations. And when, as shownin FIG. 28, external commands are input randomly, the internal operationcycle used for refresh operations cannot be specified in advance. Hence,in the fourth embodiment, the cycle used for refresh operations isdetermined according to the state of input of external commands.Specifically, the refresh command generation circuit 20 assumes a statewhich permits generation of refresh commands according to the state ofinput of external commands in sync with two consecutive external clockcycles.

Further, on the memory circuit side it is not possible to predict withwhich phase an external command will be supplied, and so the commanddecoder 11A which inputs external commands must input external commandsat both phases “a” and “b”, in sync with the external clock signal, andmust hold internal commands. Hence, as shown in FIG. 24, the commandregister 11B has a register Ia to hold internal commands for externalcommands input with external clock phase “a”, and a register Ib to holdinternal commands with phase “b”. These registers Ia, Ib hold commandsin sync with the clocks ECLKI-a, ECLK1-b, which are the external clockECLK divided by two.

The internal commands in these first stage registers Ia, Ib are held inthe later stage register 2 via the switches SWIa, SWIb in sync with theinternal clock signal ICLK1. As in the above described embodiments, theinternal clock signal ICLK1 has a frequency 8/7 times the externaloperation cycle (⅞ the cycle length). The later stage register 2 has,for example, an OR logic input, and holds the internal command held byone of the previous stage registers Ia, Ib. If an internal command isnot held by the previous stage registers Ia, Ib, the later stageregister 2 does not hold an internal command.

The command register 11B is configured in this way; as described in thecommand registers Ia, Ib of FIG. 25, in each internal operation cyclethe switches SW1, SW2 are simultaneously made conducting, and theinternal commands of both the initial stage registers Ia, Ib aresimultaneously transferred to the later stage register 2. An externalcommand is input at one of the two phases “a”, “b”, so that one of theinternal commands RD, WR is transferred to the later stage register 2and is executed by the control circuit 14.

Of the eight internal operation cycles in the expanded cycle, in thesecond internal operation cycle the contents of the ‘initial stageregister Ib alone are transferred to the later stage register 2.Similarly, in the sixth internal operation cycle, the contents of theinitial stage register Ia alone are transferred. When the later stageregister 2 holds some internal command, RD or WR, the refresh commandgeneration circuit 20 stops generation of refresh commands; if neitherof the internal commands RD, WR is held, generation of refresh commandsis permitted.

The meaning of the above operations is as follows. In the secondinternal operation cycle, only the initial-stage register Ib ismonitored, and so if an external command is not input on the externalclock signal Ib, this cycle is allocated as a refresh operation cycleRef. This operation is shown in FIG. 26. In the sixth internal operationcycle, only the initial stage register Ia is monitored, and so if anexternal command is not input on the external clock signal 5 a, thiscycle is allocated as a refresh operation cycle Ref. This operation isshown in FIG. 27.

Even if a cycle is a normal internal operation cycle, if externalcommands are not input continuously at both the phases “a”, “b” of theexternal clock ECLK, the later-stage register 2 does not hold aninternal command, and so the cycle is allocated as a refresh operationcycle. This operation is shown in FIG. 28. As in FIG. 28, when externalcommands are input randomly at both the phases “a”, “b” of the externalclock, an interval of two external clock cycles is required between theexternal commands, and so more internal operation cycles become refreshoperation cycles.

In this way, internal operation cycles are allocated as refreshoperation cycles according to the state of input of external commands.When a refresh timer signal REFTM is generated, the refresh commandgeneration circuit 20 generates a refresh command in a refresh operationcycle.

As shown in FIGS. 26, 27 and 28, eight internal clock cycles ICLK1 aregenerated for every seven external operation cycles (one externaloperation cycle is equivalent to two external clock cycles ECLK). Thesecond internal clock signal ICLK2 controlling output of read data tothe data bus DB2 lags behind the first internal clock signal ICLKI, andis generated by excluding the clock at the time of refresh operationcycles. The output latch clock ECLK L is generated by adding aprescribed lag to one of the external clock signals ECLK, according towhether the external command input is at phase “a” or “b”. Hence, theoutput latch clock ECLK L is in sync with the external clock. In FIG.26, the output latch clock ECLK L is generated by delaying the externalclock ECLK with phase “a”; in FIG. 27, it is generated by delaying theexternal clock ECLK with phase “b”. In FIG. 28, delayed external clocksignals with both phases are intermixed.

Returning to FIG. 24, when an internal command is held in either of theinitial stage registers Ia, Ib, an external address is input from theaddress register 12C. When a write command WR is held in either of theinitial-stage registers Ia, Ib, write data is input from the dataregister 135. In either case, this means that an external address andwrite data are input in sync with the 5 effective external clock.

FIG. 29 is a drawing showing the clock generation circuit applied to thefourth embodiment. FIG. 30 is the operation timing chart thereof.Similarly to the clock generation circuit of FIG. 13, an eight stageshift register 37, a multiplexer 38, a phase comparison circuit 41, adelay control circuit 42, and a DLL circuit consisting of variable delayelements D1 through D8 are provided. Differences from the example ofFIG. 13 include the fact that initial stage register control clocksignals ECLK1 a, 1 b are generated by the frequency divider 70 from theexternal clock signal ECLK; the fact that when a read command RD isgenerated, a second internal clock signal ICLK2 is generated by the NANDgate 71; and, the fact that when read commands RD1(a), RD1(b) aregenerated in the output of the initial stage command register, theoutput latch clock ECLK L is generated delayed by the timing of thefrequency divided external clock. Also, switch signals Dis a, b aregenerated with the timing of the shift register stages 2, 6.

The operation timing chart of FIG. 30 shows the case in which externalcommands are input at external clock ECLKI cycles Ia, 2 a, 3 a, 4 b, 6a. Here, the internal operation cycles 2 and 6 are refresh operationcycles. A second internal clock signal ICLK2 is generated in response tothe read command RD, and an output latch clock ECLK L is generated. Whena read command RD does not occur, the second internal clock signalICLK2, controlling output of read data from the memory core, is notgenerated. The output latch clock ECLK L is generated according to thepresence or absence of a read command RD1 in the command register 1,delayed from the frequency divided external clock signals ECLK1 a, 1 b.

FIG. 31 shows another clock generation circuit. Compared with the clockgeneration circuit shown in FIG. 29, this clock generation circuit addsswitches SW11, SW12; switch SW11 selects one of the clocks N2, 3, 4 15according to the select signals SR3, 4 of shift register 37, and switchSW12 selects one of the clock signals N6, 7, 8 according to the selectsignals SR7, 8.

FIG. 32 is an operation timing chart of the clock generation circuit ofFIG. 31. As shown in FIGS. 31 and 32, the switch SW11 selects the clockN2 when the select signal SR3 of the shift register 37 is H, selectsclock N4 when the select signal SR4=H, and otherwise selects clock N3.As a result, the phase of the output latch clock ECLKL(Ia) advancesslightly, and the internal clocks ICLK2(1), ECLK L(Ia), and ICLK2(2) aregenerated without overlap, as shown in FIG. 32. Similarly, the phase ofthe output latch clock ECLK L(2 a) lags slightly, and is generated aftergeneration of the internal clock ICLK2(3). Thus, read data is outputfrom the memory core to the data bus DB2, and the operating margin forlatching by the output register 134 can be increased. The configurationand operation of switch SW12 are similar. That is, the switch SW12selects clock N6 when SR7=H, selects clock N8 when SR8=H, and otherwiseselects clock N7.

FIG. 33 is a drawing showing a refresh command generation circuitapplied to the fourth embodiment, and operation thereof. Thisconfiguration differs from the refresh command generation circuit shownin FIG. 23 in that the refresh clock REF CLK is generated in response toan internal read command RD and write command WR. That is, the internalclock signal ICLK1 controlling the start of internal operation cyclespasses through a small delay circuit 82 before being supplied to theNAND gate 81. If the internal operation commands RD, WR are output fromthe later stage command register 2, generation of the refresh clock REFCLK is prohibited by the NOR gate 80. On the other hand, if the internaloperation commands RD, WR are output from the later stage commandregister 2, generation of the refresh clock REF CLK is permitted by theNOR gate 80.

Hence, when in the normal operation state (CKE=H), after the refreshtimer signal REFTM is generated, if the refresh clock REF CLK isgenerated, then the refresh command REF is generated, and the count upsignal UP is generated. On the other hand, in power down mode (CKE=L),if the refresh timer signal REFTM is generated, the refresh command REFis generated immediately.

As explained above, by combining the command register 11B of FIG. 24 andthe refresh command generation circuit of FIG. 33, generation ofinternal refresh commands REF is permitted according to the state ofinput of external commands.

FIG. 34 is a drawing showing another command register circuit applied tothe fourth embodiment. The command register 11B shown in FIG. 24 isprovided with two initial stage command registers in parallel,corresponding to the phases “a”, “b” of the external clock ECLK. In thecircuit example of FIG. 34, command registers are provided in series(FF1, FF2 and FF4, FF5) to hold internal commands in sync with bothphases of the external clock signal ECLK1, and gates G1, G3 are providedin place of the switches SW1 a, Ib. Respective flip flops FF3, FF6correspond to the later stage command registers.

In the command register circuit of FIG. 34, the most recent writecommand and read command decoded and generated by the command decoder11A are latched by the flip flops FF1, FF4 respectively, in sync withthe clock signal ECLK1 (not frequency divided) generated in sync withthe external clock. Commands latched in sync with the previous externalclock cycle ECLK1 are latched by the flip flops FF2, FF5 in sync withthe frequency divided internal clock ICLK1. And, in accordance with theselect signal Dis generated by the clock generation circuit 35, eitherthe logical product of the write command of the flip flops FF1, FF2(Dis=L), or the write command of the previous stage flip flop FF1(Dis=H), is held by the later stage flip flop FF3, by means of the ORcircuit consisting of the gates G1, G2, G3. The read command side issimilarly configured. The address capture signal Aen is generated by thelogical product 85 of the internal read command RD1 and internal writecommand WR1, and the data capture signal Den is generated by theinternal write command WR1.

FIGS. 35 and 36 are operation timing charts of the memory circuit forthe case in which the command register circuit of FIG. 34 is used. FIG.35 shows basic operation, while FIG. 36 shows operation for the case inwhich, as in FIG. 28, external commands are supplied randomly at clockphases “a” and “b”.

In the command register circuit of FIG. 34, the first stage register hasa series rather than a parallel configuration. Hence, as shown in FIG.35, read commands latched in sync with continuous external clock cyclesECLK1 are arranged in the flip flops FF4, FF5. As a result, the cases inwhich the read commands RD1, RD2 are in the order phase “a”, phase “b”,and cases in which they are in the order phase “b”, phase “a”, occur inalternation. Hence, in FIG. 34, in place of the switches SWIa, Ib, onlythe commands RD1, WRI of the initial stage flip flops FF1, 4 are alwayslatched by the later stage flip flops FF3, FF6. That is, the switchsignal Dis becomes H level at second and 6th internal operation cycles,the gates G1, G3 do not allow the output of flip flop FF2, FF5 totransfer to FF3, FF6. Through this configuration, as shown in FIG. 35,in the second internal operation cycle, the command on the phase Ib sideis held in the later stage flip flop FF6, and, in the sixth internaloperation cycle, the command on the phase 5 a side is held in the laterstage. That is, the operation is effectively the same as that of FIG.25.

In the case of random input of external commands in FIG. 36, effectiveinternal commands are held within bold frames, and the internaloperation cycles 1, 4, 7 are allocated as refresh operation cycles. Whenexternal commands are input consecutively at the external clock phase“a”, the internal operation cycle 2 is allocated as a refresh operationcycle, as in FIG. 26; when external commands are input consecutively onthe external clock phase “b”, the internal operation cycle 6 isallocated as a refresh operation cycle, as in FIG. 27. If, during theallocated refresh operation cycle, a refresh timer signal REFTM isgenerated, the refresh command REF is generated, and the refreshoperation is performed.

FIG. 37 is a drawing of a clock generation circuit for the case in whichthe command register of FIG. 34 is used. FIG. 38 is the operation timingchart thereof. Compared with the example of FIG. 29, the clockgeneration circuit of FIG. 37 differs in that the select signal Dis isgenerated by the NOR gate 85 and later stage inverter as the logicalproduct of the timing of the second and sixth cycles of the shiftregister 37, and in that, when a read command RD1 is generated, theoutput latch clock ECLK L is generated by delaying the output clockECLK1. By employing a series circuit configuration for the commandregister of FIG. 34, the circuit to generate the output latch clock ECLKL can be simplified. This can also be applied to the output latch clockgeneration circuit of FIG. 29. As explained before, the switch signalDis becomes H level at 2nd and 6th internal operation cycle, the commandof front stage flip flop FF1, FF4 only transfers to the back stage flipflop FF3, FF6.

Compared with FIG. 30, in the operation timing chart of FIG. 38, thereexists no frequency divided clock signals ECLK1 a, 1 b, and the time tohold the read command RD1 in the initial stage command register is halfas long. The combination of external commands in FIG. 38 is the same asin FIG. 30, and so overall operation is the same. That is, duringrefresh operation cycles REF, the internal clock ICLK2 is not generated,and the output latch clock ECLK L is generated after a fixed delay,according to the read command RD1.

Fifth Embodiment of the Invention

A fifth embodiment of the invention is a memory circuit for the case inwhich, for external operation cycles, external clock cycles are ⅓, thatis, the frequency of the external clock is three times as great as theinternal clock. For example, a memory device with an external operationcycle of 30 ns can be mounted in a system with a clock cycle of 10 ns.

FIG. 39 is a configurational diagram of the memory circuit of the fifthembodiment of the invention. Compared with FIG. 24 showing the fourthembodiment, in FIG. 39 the configuration of the command register 11B isdifferent. In FIG. 39, the external clock ECLK has three times thefrequency, and so the command register 11B comprises three parallelfirst stage registers Ia, Ib, Ic, and switches SWIa, Ib, Ic.Consequently, the clock signals ECLK1 a, b, c, obtained by ⅓ frequencydivision of the external clock ECLK, control the timing of the firststage register command capture. Otherwise, the configuration is the sameas in FIG. 24.

FIG. 40 is a drawing showing the flow of signals in the memory circuitof FIG. 39; FIG. 41 shows operations for the case in which externalcommands are input randomly with phases “a”, “b”, “c”. Here an expandedcycle consists of five external operation cycles, and within thisexpanded cycle, six internal operation cycles are generated. Sequentialinternal commands are held in the first stage registers Ia, Ib, Icwithin the command register IIb, according to the three phase clockECLK1 a, b, c obtained by ⅓ frequency division of the external clockECLK. Via the switches SWIa, Ib, Ic, cycles to transfer to the laterstage register 2 the logical sum of all commands with phases “a”, “b”,“c”, and cycles to transfer the logical sum of commands with thesequential phase combinations changed among bc, ca, ab are generated inalternation. Therefore, as shown in FIG. 40, the logical sum of commandsat phases “a”, “b”, “c” is transferred at the internal cycles 1, 3, 5,and the logical sum of commands at either phase bc, ab, ca istransferred at the internal cycle 2, 4, 6. It is also possible toconsecutively generate a plurality of cycles to transfer all logicalsums, but due to space limitations in FIG. 40, the shortest case of asingle cycle is shown.

As shown in FIG. 40, in the internal operation cycle 2, the logic sum ofcommands with phases Ib, Ic is transferred to the later stage register.Hence, when external commands are input in the shortest cycle in syncwith phase “a”, the second internal operation cycle becomes a refreshoperation cycle. Similarly, when external commands are inputconsecutively in sync with phase “b”, the sixth internal operation cyclebecomes a refresh cycle. When external commands are input consecutivelyin sync with phase “c”, the fourth internal operation cycle becomes arefresh cycle.

FIG. 41 shows operation for the case in which external commands areinput with phases 1 a, 2 a, 3 b, 4 b, 5 c. Effective internal commandsare generated within bold frames in the command register. Hence, theinternal operation cycles 2, 6, within which effective commands are notgenerated in the later stage command register, become refresh operationcompatible cycles REF. If the refresh timer signal REFTM is generatedwith this timing, the refresh command generation circuit 20 generates arefresh command REF.

FIG. 42 shows another command register circuit applied to the fifthembodiment. This command register circuit 11B is an example in which thefirst stage registers are connected in series in three stages,corresponding to the two stage series connection of FIG. 34. In FIG. 42,read commands are latched by the flip flop FF10 in sync with the clockECLK1, which is synchronized with the external clock ECLK, and aretransferred in sequence to the later stage flip flops FF11, FF12. Thelogical sum of the outputs RD1, RD2, RD3 of these three flip flopspasses through the gates G3, G5 and is transferred to the later stageregister FF13. When the select signal Dis goes to H level, the outputRD3 of the third stage flip flop FF13 is deleted by the gate G3, and thelogical sum of the remaining outputs RD1, RD2 is transferred to thelater stage register FF13. Configuration and operation are similar onthe write command side as well.

FIG. 43 is a drawing showing the flow of signals in FIG. 42. Comparedwith FIG. 40, the time for which the commands RD1, 2, 3 are held in eachof the command registers is shorter, and shifting in order is performedin sync with the external clock ECLK1. Otherwise, operation is the same.In the case of FIG. 43, the commands RD1, 2, 3 are shifted in order, andso by selecting the phase of the select signal Dis, the commands RD1,RD2 correspond to the external commands at phases cb, ba, ac, thereforethe command register of FIG. 42 corresponds to the command registercircuit shown in FIG. 42 which takes the logical sum of the two commandsRD1, 2 among the three commands RD1, 2, 3. In this case also, theinternal operation cycle 2 becomes a refresh operation cycle whenexternal commands are input consecutively with phase “a”.

FIG. 44 shows operations for the case in which external commands areinput in sync with the external clock at Ia, 2 a, 3 b, 4 b, 5 c. Thisfigure corresponds to FIG. 41. Differences from FIG. 41 include the factthat the length of the bold frame indicating effective commands in thecommand register is shorter. Otherwise they are the same, and effectivecommands are not held in the internal operation cycles 2, 6, so thatthese cycles are allocated as refresh operation cycles. In this casealso, if a refresh timer signal is present, a refresh command isgenerated.

If the fifth embodiment is expanded, a memory circuit can be configuredcorresponding to an external clock which has L times the externaloperation cycles (where L is four or greater). In this case, generationof a refresh command is permitted depending on the circumstances ofexternal commands input in sync with L consecutive external clockcycles. In this case, if a refresh timer signal is generated to indicatea time at which the refresh operation should be performed, the internaloperation actually becomes a refresh operation.

Another Clock Generation Circuit

FIGS. 45, 46 and 47 are diagrams showing another clock generationcircuit. As shown in FIG. 45, this is applied to cases in which thecycles of the external clock ECLK are sufficiently short with respect toexternal operation cycles Ecyc and internal operation cycles Icyc, andexternal operation cycles Ecyc and internal operation cycles Icyc areinteger multiples of the external clock ECLK cycles. In the example ofFIG. 45, the external operation cycles Ecyc are five times the cycles ofthe external clock ECLK, and internal operation cycles Icyc are fourtimes as long. Hence, an expanded cycle Lcyc has four external operationcycles Ecyc, and five internal operation cycles Icyc. In this case, anexternal command RD may be supplied in sync with any of the rising edgesof the external clock ECLK, but at least four external clock cycles ECLKmust be inserted between adjacent external commands.

In a case like the above, as shown in FIG. 46, the clock generationcircuit does not require a DLL circuit comprising variable delayelements, a phase comparison circuit, and a delay control circuit. Thatis, internal clock signals can be generated based on the external clockECLK.

Compared with the clock generation circuit shown in FIG. 13, the clockgeneration circuit of FIG. 46 has a shift register 37 and multiplexer 38as well, but does not use a DLL circuit. Instead, signals N1 to N5 aregenerated by taking the logical AND of a clock ECLK1 generated from theexternal clock ECLK, and the output of the shift register 90. As shownin the operation timing chart of FIG. 47, the first shift register 90performs shifting in sync with the external clock signal ECLK1. Hence,the clock signals N1 to N5, generated by taking the logical product ofthese shift signals and the external clock ECLK1, are similar to theoutputs N1 to N9 of the DLL circuit of FIG. 13. By selecting these clocksignals N1 to N5 using the output of the second shift register 37, aninternal clock signal ICLK1 can be generated having cycles four times aslong as the external clock ECLK1. Also, the second internal clock ICLK2which controls the timing for output of read data from the memory coreto the data bus DB2 is generated, through the flip flops 91, 92, 93 andNAND gate, with timing delayed by two external clock cycles.

When using the clock generation circuit of FIG. 46, an appropriateoperation cycle among the five internal operation cycles should beutilized for refresh operations. Further, internal operation cyclesshould be used for appropriate refresh operations according to thecircumstances of external commands input in sync with the externalclock.

First Modification of The First embodiment

FIG. 48 is a drawing showing a memory circuit according a modificationof the first embodiment. In the first embodiment shown in FIGS. 2 to 10,the memory controller executes an operation corresponding to an internalcommand in sync with an external clock signal during a normal state, andafter a refresh command being issued, the memory controller executesoperations corresponding to the refresh command and the internal commandasynchronous with the external clock. In the asynchronous operation, thememory cell array operation is executed according to the internaloperation cycle shorter than the external command cycle, which is fasteroperation than the normal operation.

On the other hand, in the modification of FIG. 48, a clock generationcircuit 102 for generating a faster clock signal ICLK3 than the externalclock signal ECLK1 and a switch circuit SW are added. And these circuits102 and SW generate, during a normal state, an internal clock signalICLK2 synchronous with the external clock signal ECLK, and an internaloperation is controlled in sync with the internal clock signal ICLK2.And after a refresh command being issued internally, these circuit 102and SW generate an internal clock signal ICLK2 synchronous with a fasterclock signal ICLK3 than the external clock signal ECLK, so that theinternal operation is controlled in sync with the internal clock signalICLK2. Then after the internal operation cycle catching up the cycle ofthe external clock signal, the circuits 102 and SW returns to the normaloperation state so as to generate the internal clock signal ICLK2 insync with the external clock signal ECLK.

In order to switch the internal clock signal ICLK2 for the internaloperation timing, the memory circuit of FIG. 48 includes OR gate 104 forgenerating a logical sum of the read command RD, write command WR andrefresh command REF and a comparator 103 for comparing a timing of Hlevel of the output Si of the gate 104 and a timing of H level ofcommand reception signal CMDEN. While the timing of the commandreception signal CMDEN is faster, it is determined as a normal state andthe operation switch signal OSW becomes L level so that the clock signalECLK1 in sync with the external clock signal ECLK is output as theinternal clock signal ICLK2. Further, while the timing of the generationof any command (output S1 of OR gate 104) is faster, it is determined asa faster operation mode and the operation switch signal OSW becomes Hlevel so that the faster clock signal ICLK3 generated by the clockgeneration circuit 102 is output as the internal clock signal ICLK2.

FIG. 49 is an operation timing chart of the modification of FIG. 48. Inthis example, a read command RD is supplied in sync with an externalclock signal ECLK1. In response to this, the command register 11 holdsand output the read command. And in response to the refresh command REFgenerated by the refresh timer 21 in a prescribed cycles, the refreshcommand generation circuit 20 generates the refresh command REF. On theother hand, the controller 14 generates a command reception signal CMDENevery time when an internal operation of the command is finished, so asto receive a next command.

The comparator 103 compares a rising edge of the command receptionsignal DMCEN and a rising edge of the read command RD, write command WRor refresh command REF (or starting timing of H level of thesecommands), makes the operation switching signal OSW L level as a normalmode when the command reception signal CMDEN is faster, and makes theoperation switching signal OSW H level as a faster operation mode whenthe timing of the commands is faster. That is, the switching circuit SWselects the external clock ECLK1 or the faster clock ICLK3 depending onthe switching signal OSW and output the internal clock signal ICLK2. Thememory control circuit 14 controls the memory core 15 in sync with theinternal clock signal ICLK2. However, the timing of the read data andthe write data is controlled in sync with the external clock ECLK1.

In the example of FIG. 49, internal operations of read command RD OA toRD A2 are normal operation state and the internal clock signal ICLK2 insync with the external clock signal ECLKI is generated. However, afterthe refresh command REF is issued, the internal operations become afaster operation state, the internal clock signal ICLK2 in sync with thefaster clock signal ICLK3 is generated. In the mean time, the internaloperation cycle catches up the external clock cycle at the read commandRD A7 and the internal operation returns to the normal state after theread command RD A8.

Second Modification of the First Embodiment

FIG. 50 is a drawing showing a memory circuit according to anothermodification of the first embodiment. This modified memory circuit is arandom access memory for operating asynchronously without being suppliedwith an external clock signal. The operation of the first embodiment isapplied to the asynchronous type DRAM.

Asynchronous type DRAM has a specification of the minimum externalcommand interval upon which the external commands are permitted to besupplied. Therefore, a memory controller can not supply the externalcommands to the memory device upon shorter time interval than theminimum external command interval defined in the specification. And thememory circuit executes an internal memory operation upon receiving theexternal command and output read data. The specification also defines anaccess time between a read command input and a read data output.Therefore, the memory controller fetches the read data at a timingslightly delayed from 5 the access time after supplying the externalcommand. Upon fetching the read data, the memory controller replies tothe memory circuit a notice signal informing the read data fetchcompletion.

According to the first embodiment, the memory device operates inresponse to the external command in a normal state, and when issuing theinternal refresh command, operates according to an internal operationcycle asynchronous with the external clock and shorter than the cycle ofexternal clock. Therefore, the memory device 15 operates in a slowoperation mode in the normal state, and operates in a fast operationmode when the internal refresh command is issued. This operation can beapplicable to the asynchronous DRAM easily.

Comparing to the memory circuit of FIG. 2, the memory circuit of themodification of FIG. 50 does not include a clock buffer circuit, butincludes a delay circuit 100 for generating an output timing signalSOUT. The data I/0 buffer register 13 output read data in response tothe output timing signal SOUT. This delay time of the delay circuitcorresponds to the above mentioned access time. The structure except forthis is the same as FIG. 2.

The memory control circuit 14, the same as FIG. 4, generates controlsignals corresponding to the supplied command and generates a commandreception signal CMDEN upon finishing the memory array operation so asto receive the next command and generate the control signalscorresponding to the next command. According to the modification, thememory array operation period corresponding to the internal operationcycle is designed to be shorter than the minimum external commandinterval. As a result, in a normal state, the internal operation cyclecan be repeated in sync with the input timing of the external command.On the other hand, when the refresh command is issued internally, theinternal operation cycles can be repeated in serial asynchronous withthe input timing of the external command. That is, in the normaloperation state, the memory circuit becomes a slower operation mode insync with the external command timing, whereas, when the internalrefresh command is issued, the memory circuit becomes a faster operationmode according to the internal operation cycle. When the internaloperation cycle catches up the external command timing, the memorycircuit returns to the slower operation mode.

FIG. 51 is a timing chart showing an operation of the modification. FIG.51A shows a normal operation state which is the slower operation mode insync with the external command timing. As shown in the drawing, thememory cell array operation period tmca is designed to be shorter thanthe minimum external command interval tecmd. Therefore, when the memorycell array operation, which is the internal operation, starts in syncwith the external command, the operation finishes before the nextexternal command being supplied. Even though the command receptionsignal CMDEN raises to H level in response to the end of the memory cellarray operation, the next external command (RD, WR) is not supplied yetat this time. Upon the next external command being supplied afterprescribed time being elapsed, the next memory array operation starts inresponse to the supplied command. Even though asynchronous DRAM, sincethe internal operation cycle tmca is shorter than the minimum externalcommand interval tecmd, the internal operation cycle can be repeated insync with the external command timing in the normal operation state.

FIG. 51B shows the faster operation mode asynchronous with the externalcommand timing when the internal refresh command REF is issued. Sincethe internal refresh operation is interrupted, the memory arrayoperation can not finish until the next external command timing.Therefore, the next memory array operations are executed in response tothe rising of the command reception signal CMDEN continuously. That is,the internal operation cycles are repeatedly executed without waitingthe next external command timing.

FIG. 52 is an operation timing chart in case where the normal operationstate is transferred into the faster operation mode upon generation ofthe internal refresh command. FIG. 52 is the same as the one eliminatingthe clock signal CLK1 from the operation timing chart of FIG. 5. Whenthe first read command RD(AO) is generated, the previous memory cellarray operation is finished and the command reception signal CMDENbecomes H level already. Therefore, the internal memory cell arrayoperation starts in response to the timing of the read command RD(AO).

This is the cycle No. 1. The memory cell array operation comprises, asdescribed before, word line driving (control signal OWL), senseamplifier activation (OLE), column gate selection (OCL), and pre charge(OPRE). When the pre charge control signal is generated, the commandreception signal CMDEN becomes H level.

According to FIG. 52, the refresh timer signal REFTM becomes H levelduring the first read operation so as to inform the timing of theinternal refresh. In response to this, the internal refresh commandREF(Aa) is generated. And when the memory cell array operation for thefirst read command is finished and the command reception signal CMDENbecomes H level, the refresh command REF(Aa) is already generated,therefore, the refresh operation for the refresh command can startimmediately. This is the cycle No. 2. The refresh operation is a readoperation without having column gate selection.

Further, since during the internal refresh operation, the next readcommand RD(A1) is supplied, the internal read operation startscontinuously upon finishing the refresh operation. This is the cycle No.3.

FIG. 53 is a timing chart of the slow operation mode and the fastoperation mode according to the present modification. This is the sameas one eliminating the clock signal CLK1 from FIG. 6. That is, this isclock asynchronous DRAM, the external command CND is supplied with aninterval equal to or longer than the minimum external command interval,and read data is output at DQ terminal after a prescribed delay timeDELAY from the external command supply. In FIG. 53, the operation duringthe first three read commands RD AO to RD A2 is the slower operationmode in which the internal operation is executed in sync with theexternal command. And the operation during the read command RD A4 to A7after generation of the refresh command REF is the faster operation modein which the internal operation cycles are repeated continuously. Whenthe internal operation cycle catches up the external command timing, theoperation returns to the slower operation mode in sync with the externalcommand after the read command RD A8.

As described above, according to the first embodiment, either the casewhere the external commands are supplied in sync with the externalclock, or the case where the external commands are suppliedasynchronously, since the internal operation cycle is designed to beshorter than the external operation cycle or the minimum externalcommand cycle, the internally generated refresh command can beinterrupted among the normal commands (read or write).

Thus, by means of this invention, in a clock-synchronous type integratedcircuit, prescribed internal operation cycles not corresponding toinstructions from outside can be generated and executed autonomously, sothat the control of an external controller can be made simple.

Also by means of this invention, in a memory circuit requiringrefreshing, even in the normal operating state, refresh operation cyclescan automatically be generated internally without applying refreshcommands from an 15 external controller.

The scope of protection of this invention is not limited to the abovedescribed aspects, but extends to the inventions described in the Claimsand to equivalent entities.

1. A memory circuit requiring refresh operations, comprising: a memorycore having memory cells; a first circuit which receives a commandsupplied in synchronization with an external clock signal, and whichgenerates a first internal command internally; a second circuit whichgenerates a refresh command internally in a prescribed refresh cyclewhich is larger than the cycle of said external clock signal; and amemory control circuit which includes a first internal operation cycleand a second internal operation cycle shorter than said first internaloperation cycle, executes control corresponding to said first internalcommand according to the first internal operation cycle, and when saidrefresh command is issued, sequentially executes a control correspondingto the refresh command and a control corresponding to said firstinternal command according to the second internal operation cycle. 2.The memory circuit according to the claim 1, wherein the memory controlcircuit executes the corresponding control according to the firstinternal operation cycle while a finish timing of the internal operationis faster than a generation timing of the first internal command or therefresh command, whereas, executes the corresponding control accordingto the second internal operation cycle while the generation timing ofthe first internal command or the refresh command is faster than thefinish timing of the internal operation.
 3. An integrated circuit deviceoperating in synchronous with a clock signal, comprising: a firstcircuit which generates a first internal command internally according toa command externally received; a second circuit which generates a secondinternal command internally, in a prescribed cycle larger than thecycles of an external command cycle; and an internal circuit whichincludes a first internal operation cycle according to which an internaloperation is executed in synchronous with the external operation cycle,and a second internal operation cycle according to which the internaloperation is executed in a shorter cycle than the first internaloperation cycle; wherein the internal circuit executes an operationcorresponding to the first internal command according to the firstinternal operation cycle in a normal state, and executes an operationcorresponding to the first and second internal commands according to thesecond operation cycle during a prescribed period after generation ofthe second internal command.
 4. A memory circuit requiring refreshoperations, comprising: a memory core having memory cells; a firstcircuit which receives external commands supplied with an interval equalto or longer than a minimum external command cycle, and which generatesa first internal command internally; a second circuit which generates arefresh command internally in a prescribed refresh cycle which is largerthan the minimum external command cycle; and a memory control circuitwhich executes internal operation corresponding to the first internalcommand according to an internal operation cycle shorter than theminimum external command cycle; wherein the memory control circuitexecutes an internal operation corresponding to said first internalcommand in response to a timing of the external command while a finishtiming of the internal operation cycle is faster than the timing of theexternal command, and when said refresh command is issued, sequentiallyexecutes control corresponding to the refresh command and controlcorresponding to said first internal command according to the internaloperation cycle.
 5. The memory circuit according to the claim 4, whereinwhen the internal operation is finished, the memory control circuitreceives the first internal command generated by the first circuit orthe refresh command generated by the second circuit, and executes thecorresponding internal operation.
 6. A memory device receiving externalcommands supplied with an interval equal to or longer than a minimumexternal command cycle time, comprising; a memory core including DRAMcells and having an internal operation cycle time shorter than theminimum external cycle time; an refresh command generation circuit forinternally generating a refresh command for refreshing the DRAM cells;and a control circuit receiving the external command and the refreshcommand for controlling the memory core such that the memory coreinitiates to execute an internal operation cycle upon a receipt of theexternal or refresh command in case where the control circuit does notreceive the external and refresh commands at the beginning of a commandreception period, and the memory core initiates to execute the internaloperation cycle immediately after entering the command reception periodin case where the control circuit receives the external or refreshcommands at the beginning of the command reception period.
 7. The memorydevice as claimed in claim 6, wherein there is a latent period between areception timing of the external or refresh command the beginning timingof the command reception period in case where the control circuit doesnot receive the external and refresh commands at the beginning of thecommand reception period.
 8. The memory device as claimed in claim 6,wherein a plurality of the internal operation cycles are sequentiallyexecuted while the control circuit receives the external or refreshcommands at the beginning of a command reception period.
 9. The memorydevice as claimed in claim 6, the memory device being an asynchronoustype DRAM which is not supplied with an external clock signal.
 10. Thememory device as claimed in claim 6, wherein the external command is aread command or a write command.
 11. The memory device as claimed inclaim 6, wherein the refresh command generation circuit generates therefresh command both in a normal operation mode and a power down mode.12. The memory device as claimed in claim 6, wherein the internaloperation cycle includes an activation of a word line, an amplificationof bit line voltage, an inactivation of the word line and a precharge ofthe bit lines.
 13. The memory device as claimed in claim 6, wherein thecontrol circuit receives a command reception signal which is generatedin response to a precharge signal for precharging bit lines.
 14. Thememory device as claimed in claim 13, wherein a transition of thecommand reception signal corresponds to the beginning of the commandreception period.
 15. The memory device as claimed in claim 6, furthercomprising; a command register for storing the external command andsupplying the control circuit with the external command.
 16. The memorydevice as claimed in claim 15, wherein the command register is resetupon an initiation of the internal operation cycle.